Diagnosing Cruise Control Failure
As far as the cruise goes, the very first thing I would check is to make sure that the actuation cable is present and is fairly taught. It is the lowest cable on the throttle linkage if I'm not mistaken and it comes from the left front fender area. The vacuum servo is in the left front fender behind the wheel. It is easy to get to; just take the wheel off and pop the plastic inner fender out. It is held in by six or eight small screwbolts. That was just for your information because you may never need to go in there. If the linkage is very loose, (unlikely the problem) you can adjust it at the linkage with the nut that is there. It is fairly obvious. The next thing to check is the vacuum lines. Vacuum leaks happen often and will cause failure of the cruise. You will see 2 lines running down from the brake booster into the left fender. They go to the cruise servo. You need a vacuum pump to test them. Just hook up the pump and give it a few strokes; the lines should hold vacuum. One line will pump up right away and the other you will have to pump for a while (about 10 strokes) because it is the vacuum reservoir located next to the cruise servo and it has a larger volume. If they hold vacuum, that is good and bad. It means they are fine, but your problem is electrical. If they don't hold find out why. It could just be that the lines are bad or popped off- easy fix just replace them with standard vacuum hose. It could also be that the vacuum servo or the reservoir is leaking. Not as easy but probably fixable without replacing. I've had mine apart so if you get there and find one of those is bad meaning not holding vacuum, let me know and I can definitely help you there. If everything checks out here, and it probably will, then your problem is either in the wiring or most likely of all BAD NEWS - your computer is dead. The factory service manual contains a step by step guide to testing the electrical signals to the computer. All you need is a multimeter and it is very straightforward. In my case I found 2 problems. First I found a short at the vacuum servo and I thought I had the problem down. I disassembled the servo and rewired it internally. That's not as impressive as it sounds; its a very simple servo switch. The short went away but the cruise still didn't work. I diagnosed further and found the computer to be faulty which happens a lot. I haven't checked too much into a replacement but I know they are expensive $400-600 new.
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